Optical Isolation

First impression very positive.  I'll need to give a bit of time to have more meaningfull thoughts.

Technically coax should be better, since transitions are faster, hence system noise (jagged edges on transitions slopes) does not convert to timing jitter, but coax is prone to reflections on characteristic impedance boundaries (that adds/changes shape of transitions) and transfers digital noise by direct connection of the grounds. It can also create ground loops.  Optical is free of all these problems but transitions are likely 10x slower making system noise to convert to timing jitter easier (noise riding on the signal = jagged edge = variation in time of the threshold point).  If your system is electrically quiet or your DAC has good jitter suppression I would try optical first (that's what I have) - less hassle and cheaper.  Otherwise you need to compare different coax cables.  One with closest impedance match (not necessarily the most expensive one) will sound the best - cleanest (since jitter converts to noise).  Also 1.5m-2m can sound better than 1m (because reflections coming from the end of the cable, if any, will likely miss/be late the edge that started them) 

Any device, like streamer or WiFi receiver (like my Airport Express) should receive just bit perfect data, but can have different quality of electronics to convert this data to music (to add timing) and output it (strong, fast drivers, quiet power supply etc.)  IMHO it is impossible to express it in numbers - you need to listen.

I run the opticalRendu player/ endpoint along with the optical module to get my fiber to optical transition hook up.  A nice set up to clean up the potentially noisy ethernet.  I started with the sonicTransporter I5 as a roon core.  Not sure how to run the rendu without Roon as it is a player only.  I'm very happy with this and the latest 2.0 Roon update was really nice for sound quality upgrade.  Call Andrew Gillis at SGC and can get you the info you need.

@kijanki - Thanks, not sure I understand it all, except the "you need to listen" part. I will heed your advice!

@gkr7007 - I have communicated with Andrew in the past, but not really wishing to go with Roon at this time.

@carlsbad - How's that new switch sounding Jerry? Interesting option.

@navyachts You aren't limited to Roon only if you go with an opticalRendu. Rendus are compatible with any DLNA and UPnP software like Lumin App, Linn, etc. Some of those have Qobuz and Tidal integrations. 

You could go with a Rendu, and always add Roon later if you like. Cheers,

Spencer